.223 twist

mrmiskin · #1 09-04-2007, 07:01 AM

How much does accuracy suffer when shooting the heavier bullets , above 55 gr, in a 1 in 12 twist barel. I have heard different stories and have been told the rule of thumb is above 55 gr requires a 1 in 9 twist. thanks

Rapier · #2 09-13-2007, 12:42 PM

In general, as you increase the weight for a given diameter you increase the length. The length of the bullet is what is used to determine the proper twist rate need to stabalize that bullet.

According to my computer programs, the optimum twist rate for the following Sierra .224 bullets applies:
53 gr MK 10.75
55 gr Var 10.45
60 gr Var 9.52
63 gr Var 9.9 This bullet is shorter than the 60
69 gr MK 8.3

My experiance is that you can get away with one number plus or minus from the optimum rate. However when you go up or down two, things may get real "if'y".

As to how bad accuracy is effected by using a .224 bullet past the weight to twist ratio that will suport that bullet weight, that depends on the distance and use. A full auto AR or 16 with a 1-12 twist and 69 gr bullets might be great at 25 yards. But do not expect head shots at 300 meters. You might see oblong holes in paper as close as 50 meters in such an instance.

The original 223/5.56 round in the M-16 which had such a nasty reputation for bad wounds was a 55 gr FMJ bullet (shorter than the 55 Var and same length as 53 gr MK) in a 1-12 twist barrel. The bullet was barely stable, but it remained barely stable out to 300 meters.
Ed

Catfish · #3 09-13-2007, 08:31 PM

Each barrel is different. Some do as they are suposed to and others not quite. I had a 1 in 14 twist that did pretty well with 55 gn. bullets. By that I mean it would shoot abt. 3/4 moa and some times better. A 12 twist should shoot 55 pertty well, but you`ll not be sure untill you try them. I`m sure that barrel harmonics figures in the equation, I just don`t know how. I would guess that the flat base 55`s will shoot better than a boat tail bullet though.

mrmiskin · #4 09-14-2007, 06:04 AM

Thanks for the information it is greatly appreciated.

Ridge Runner · #5 09-21-2007, 07:39 PM

I normaly don't post on this forum for personal reasons but I wanted to tell ya, overstabilization doesn't effect accuracy enough to worry about, understabilization is disastous.
Go with an 8 twist unless you plan on shooting bullets 50 gr and less exclusively. I have no trouble and see no difference in accuracy from 50 to 75 gr in my 8 twist 223
RR
RR